that's in the Gameplay.CONSTANTS file. However, DO NOT MESS WITH THE DAMAGE PERCENT BONUSES!!!!! That can SERIOUSLY MESS UP your game or mod. The lines you would want are denoted by the prefix 'ChanceToHitTargetType' (or close to that), under the 'DamageData' section of the file. It's not far down, pretty near the top.
A tip on target types- CAPITALSHIP is Caps, Frigs, Cruisers, Structures, Starbases, Planets; i.e. anything not Strikecraft. Interceptors are fighters and Bombers are, well, Bombers.